Maybe It Was A Mistake To Buy A Fighting Fish

Hello,

I am new to the forum and new to keeping fish.  When first starting out, I assumed I didn't have to do much research and could rely on pet store advice.  I'm not sure that worked well. 

Anyway, my tank is a 40l pets at home one and the water levels are all mostly OK, but the ph is high at about 8.  My real problem is that the first fish I bought was a bright white Molly.  Later, I bought a betta and after a few casualties they are they only two fish in the tank. 

The problem is that the betta is constantly chasing the Molly and it's no fun.  I've tried buying a bunch of new plants to provide hiding places and moving everything around to shake up the territories a bit.  That worked well for a few days but he is back at it again.  I'm worried he's eventually going to kill the Molly although he rarely ever catches up with the Molly. 

I'm worried that the Betta was really a bad choice as now we are pretty limited in what other fish we can buy.  I'd like a peaceful tank and don't want to watch any fish get bullied to death. 

Any ideas?  I think it is an option to take the betta back to the store I bought him from. 

Thanks,

Jim